Studies with rodent models have shown that in utero exposure to high selenium is teratogenic to the nervous system and high environmental selenium has been associated with an increased incidence of motor neuron disease in humans and livestock. The underlying mechanism causing these neuropathologic processes are unknown. Given the increasing public use of selenium supplements there is also an increasing potential for significant human in utero exposure. We propose to identify the protein signaling pathways activated by selenium in an invertebrate model using a genetic approach as a first step toward understanding the potential mechanisms responsible for selenium neurotoxicity. In Caenorhabditis elegans exposure to selenomethionine (SeMet) causes progressive paralysis, decreased fertility, and growth retardation of adults derived from selenium-exposed embryos. Our initial invertebrate studies suggest that part of the disease mechanism involves activation of caspase and a P/Q-type calcium channel related to a mammalian channel associated with neurodegeneration. Chemical and transposon mutagenesis will be used to identify more genes encoding proteins conferring sensitivity and resistance to the effects of SeMet. The C. elegans model provides the advantages of a completely sequenced genome, a huge collection of reference gene mutations, and diverse techniques for gene disruption and identification. Applicability of invertebrate work will be tested immediately in a human motor neuron cell-line using pharmacologic and RNAi inactivation of proteins identified through the invertebrate genetics. In addition, genes activated by selenium in the motor neuron cell-line will be identified by use of microarray expression studies and RT-PCR. In cases where the genes identified by microarray studies have not been genetically identified in the invertebrate work, these candidate selenium-signaling proteins will be disrupted by RNAi in C. elegans to look for a phenotype suggesting the role of these proteins in invertebrate selenium signaling. Initial studies of selenium effects in a mammalian cell-line have already confirmed that selenium-mediated regulation of the apoptotic cascade is evolutionarily conserved between our two models. It is hoped that interlocking the discovery process in an invertebrate and mammalian model will accelerate the identification of mechanisms underlying selenium-mediated neurodegeneration and identify new therapeutic targets.